The Innova 1303 multipoint sampler and doser (Innova Airtech Instruments, Denmark) was used in combination with the Innova 1312 multi-gas monitor and 7620 tracer gas monitoring application software (Innova Airtech Instruments, Denmark). Both instruments were calibrated before the experiments. The Innova 1303 unit is normally used for office sized room measurements and can only analyse samples from a maximum of 6 locations and release a maximum dosing volume of 15 ml/sec. The 7620 application software enables remote control from a personal computer of the gas monitor (1312) and sampler/doser unit (1303). All measurements were recorded in the 7620 program and later transferred to Excel for storage and processing. Pure SF6 tracer gas (100% concentration) was injected in all tracer gas experiments.
The multi-gas monitor was set up to measure SF6 from each of the 6 sample locations, with a whole sampling cycle including sample analysis and cell flushing lasting ≈10 minutes. Once again, PTFE tubing (3mm diameter and 0.5mm wall thickness) was used for all air sampling and tracer gas dosage tasks. The PTFE tubing at all locations was no longer than 50 m and consisted of a fine Teflon dust filter installed at the beginning of each sampling line. An external pump (Innova Airtech Instruments, type EB 6000, Denmark) was also connected to the 1303 unit to increase the air vacuum rate for sample tubes.
Fig. 3- 4: Experiment 2 set-up
The main problem when conducting tracer gas measurements in naturally ventilated livestock buildings is that inlets and outlets are constantly changing. With the equipment at hand in these experiments only 6 sampling locations were available and a maximum dosage volume (15 ml/sec). Because of the very large livestock house internal air volume 3, very expensive tracer gas costs, limitations of technical equipment and constantly changing air distribution patterns inside Louisiana stall environments. A section was created within the livestock house (Fig. 3-4) and was partially separated from the livestock house with tarpolines (internal volume ≈815m3), here the gas sampling/dosing equipment were all installed. The tarpolines only very basic covered ≈ 47% of the internal transect area, were quickly installed and did not hamper farming operations. The aim of installing the tarpolines was to stabilise the air distribution patterns, reduce longitudinal flow/turbulences and increase air mixing within the livestock house so that air sampled within this section was representative of the whole internal environment. Several smoke tests were conducted to confirm sufficient mixing of livestock house air with the air mixing sub-section (Fig. 3-5). This sub-section will be referred to as the air mixing sub-section. Sampling was conducted within the air mixing sub-section from the openings of 3 chimneys (height 5.7m) and 3 lee side window locations (height 1.7m) (Fig. 3-4). The tracer gas was constantly injected from the prevailing windward side via a single point on 07-10.11.03 and via
three points on the windward side wall 12-13.11.03. On the 13.11.03 the wind direction changed from easterly to westerly, the dosing and sampling equipment swapped sides with 3 point dosing being conducted from the opposite side wall within the air mixing sub-section at a height of ≈1,7m.
Fig. 3- 5: Smoke test displays air mixing within the broiler house and air mixing sub-section
Furthermore, because of the technical limitations in this experiment it was hoped that by performing the measurements under constant weather conditions, i.e. constant transverse winds (90° wind angle of attack to the building) the inlets and outlets would remain relatively fixed and thus fresh air would mix with the injected tracer gas and outlet samples were assumed to be representative of outgoing air. It is believed that the best conditions for such measurements are in winter when air exchange rates are not too high in comparison to the high volume air exchanges occurring under summer conditions. Fortunately, the majority of measurements were conducted in autumn (07-14.11.03) with relatively constant transverse wind directions and wind velocities generally > 2ms-1 , therefore conditions were optimal.
When doing ventilation rate measurements in full sized naturally ventilated houses the actual ventilation rate is not known. A reference method giving the true value is not available, therefore it is difficult to determine the accuracy of each method. Under such circumstances a useful approach is to compare the methods with inside hygro-heat parameters and outside weather conditions, as was done in the results and discussion section.
In addition to the tracer gas method, the 2 mass balance models heat & moisture (CIGR 2002) were used for calculating the air exchange rates. In Experiment 1 (summer conditions) it was possible to test all 3 mass balance models (CO2, heat and moisture), however due to time constraints in the autumn working in line with the farmers operations, the PFTE tubing was insulated but not heated, therefore condensation occurred in the gas sampling tubes resulting in false CO2 results, so only the heat and moisture mass balance models were tested along side the tracer gas method. Because of power problems it was only possible to conduct bird activity measurements from the 12-14.11.03. These results will not be included because there is no way of validating mass balance model result improvements in naturally ventilated stalls. The effect of including activity on the mass balance model results in the mechanically ventilated stall (Experiment 3) were included, because the true ventilation rates were measured and direct comparisons could be made.
Several temperature/humidity sensors (Rotronic type HygroLog-D, Switzerland) measuring temperature and humidity were installed throughout the livestock house.
Three were positioned at the sampling locations along the wall and 1 at the dosing point, these values reflected the outside weather conditions so were not used. Normally it is recommended to use the values from sensors located in the centre of the stall (height 1,5m), but the sensor was damaged, so the 3 sensors located near the chimneys (height ~5,7m, 1 inside the air mixing sub-section and the other 2 outside) were used in the calculations. There was no difference in temperature and humidity measurements between the sensors within and outside the air mixing section. The sensors for measuring temperature and relative humidity were all checked in a climate-controlled chamber before the measurements. The climate in the room was 20°C and 40%
relative humidity, correction factors for each sensor were calculated and included in the calculations.
Because it was autumn and the weather was cool, there were heaters operating at times throughout the measurement period. At the beginning of the measurement period (07.11.03) the birds were approximately 3 weeks old, so there was no need for the heaters to operate at full capacity. After discussion with the farmer and several inspections it was clear that the brooding heaters were set up in such a way, to minimize heat consumption and evenly distribute the heat. Of the total 28 heaters in the stall (Fig.
3.6.1), seven distributed throughout the stall were functioning at near full capacity and the remaining twenty one were operating at a much lower output (~10%). In order to improve the accuracy of the heat and moisture balance calculations the consumption of natural gas by the heaters was measured and the heat output calculated. Because it was ascertained that the heaters were generally operating at 2 different output levels, 2 gas meters were fitted to two heaters with different output levels. The gas consumption was metered and noted over time and an average heat output for all heaters was calculated, this additional heat source was included in the heat and moisture balance calculations.
The external weather parameters (temperature, humidity, wind speed and wind direction) were measured hourly from a weather station (TOSS GmbH, Germany), which was located 300m away from the livestock house in the upwind direction.